Typically, an injection apparatus of a molding machine moves an injection plunger forward in a sleeve using an injection cylinder to press molding material (such as metal) out from the sleeve into a cavity formed between a pair of mold portions. The molding material is thus injected, or supplied, into the cavity. The injection, or supply, step includes a low-speed step, a high-speed step, and a pressure-increasing step.
The injection apparatus reduces the speed of the injection cylinder, which moves at a high speed in the high-speed step and then proceeds to the pressure-increasing step. At this stage, if the injection cylinder is decelerated insufficiently, the injection plunger, which is integral with the injection cylinder, strikes the mold with impact, applying excessive pressure, which is surge pressure, to the cavity. To avoid such an excessive pressure, the injection apparatus includes a speed reduction mechanism for reducing the speed of the injection cylinder. See Patent Document 1.
As shown in FIG. 8, in an injection apparatus disclosed in Patent Document 1, an injection plunger 82 is connected to a piston rod 80a of an injection cylinder 80 via a coupling 81. An L-shaped striker 83 is joined to the coupling 81. A magnetic scale 83a, which is formed by arranging magnetized portions and non-magnetized portions alternately at a constant interval, is attached to the striker 83. The injection cylinder 80 is connected to a non-illustrated hydraulic fluid tank via a fluid pressure circuit 80b. The fluid pressure circuit 80b includes a flow control valve 80c, which is driven by a pulse motor 80d. 
The injection apparatus of Patent Document 1 also includes a magnetic sensor 84 for detecting a magnetic signal of the magnetic scale 83a and a position detector 85, which counts magnetic signals detected by the magnetic sensor 84 and converts the magnetic signals into a stroke signal of the injection plunger 82. The injection apparatus further includes a speed detector 86 for converting the stroke signal from the position detector 85 into a speed signal and an acceleration detector 87 for converting the speed signals from the speed detector 86 into an acceleration signal.
The injection apparatus also includes a determination circuit 88 for detecting a time point at which speed reduction is started based on the acceleration signal, a valve opening degree setting device 89 for setting the opening degree of the flow control valve 80c, a position setting device 90 for changing injection speed, and a control command generator 91 for controlling the flow control valve 80c. 
In the injection apparatus of Patent Document 1, the striker 83 operates in conjunction with the injection plunger 82 when the injection plunger 82 moves. The magnetic sensor 84 detects a magnetic signal of the magnetic scale 83a, which is integral with the striker 83. Then, based on signals from the position detector 85, the speed detector 86, the acceleration detector 87, the determination circuit 88, the valve opening degree setting device 89, and the position setting device 90, the control command generator 91 outputs a control command to the pulse motor 80d. The opening degree of the flow control valve 80c is thus controlled to adjust the amount of the hydraulic fluid delivered from the fluid pressure circuit 80b into the injection cylinder 80. In this manner, the movement speed of the injection cylinder 80 is controlled to allow the aforementioned speed reduction to occur.